Generally speaking, water-based microemulsions containing perfumes or flavors, or yet other hydrophobic active materials, have already been reported in the prior art. Frequently, these prior known microemulsions, in order to provide proper dispersion of the oil in the water-based medium, contain large amounts of short chain alcohols, namely ethanol, or other ethanol materials.
However, ethanol is considered as a Volatile Organic Compound (“VOC”). By “VOC” what is meant is a compound defined by the Environmental Protection Agency, or by EC Directive 1999/13/EC (Solvent Emissions Directive) as organic compound having a vapour pressure of 0.01 kPa or more at 293.15 K (20° C.), or having a corresponding volatility under particular conditions of use.
In the fragrance field, there is a need and there would be advantages in finding alternatives to these conventional microemulsions, in particular ethanol-free alternatives, while retaining all of the microemulsion's positive aspects, such as sensorial performance, sprayability, diffusity, and skin feel, which are associated with the presence of such short chain alcohols and in particular with ethanol.
The replacement of ethanol is very challenging for the perfumer due to the beneficial characteristics of this ingredient in perfume formulations. Indeed ethanol is an ideal solvent for perfumery ingredients, e.g. it evaporates rapidly and does therefore not disturb the odor of the perfume after its short time of evaporation. Another key characteristic of ethanol is its wetting power, which allows good spreadability of the perfume on the skin and in turn controls the diffusion of the perfume at a later step. The fast evaporation of ethanol also adds a somewhat refreshing aspect to the formulation; a characteristic that is highly appreciated by the customer.
Low VOC microemulsions have been reported in the prior art. Generally in formulating such microemulsions, it is necessary to increase the total amount of surfactants so as to obviate the absence of VOCs, otherwise the final emulsions display a lack of clarity and/or stability problems, and this is not acceptable for the perfume and flavor applications. The increase in the amount of surfactants in the final microemulsion typically results in products containing surfactant systems that are often in large excess with respect to the solubilized oil, namely the perfume or flavor. Obviously, a large excess of surfactant is also a disadvantage for such final products, in particular for perfumes or other products intended for application to the skin, hair or surfaces such as textiles, wherein high surfactant content can lead to foamy, sticky, irritating or allergenic products that are unacceptable to consumers.
US 2006/0165739 discloses the preparation of alcohol-free microemulsions and methods for their use in cosmetic compositions. These microemulsions include a surfactant, a lipophilic and hydrophilic linker, a co-oil and can include a hydrotrope. These hydrotropes are present at a concentration between 0.001 and 30% and are used as agents that increase the solubility of other organic substances in water. Specifically, ammonium xylene sulfonate, sodium xylene sulfonate, sodium mono or dimethyl naphthalene sulfonate, and alkyl glucosides are mentioned as suitable hydrotropes.
U.S. Pat. No. 4,488,989 discloses aqueous compositions containing urea as a hydrotrope, and in particular liquid detergents of improved storage stability. Urea is used in combination with a hydrolysable ester as the storage stability promoting component. Ethanol is present in such formulations up to a concentration of 10%.
US 2011/0177995 discloses an EtOH-free microemulsion, which needs a 1/1 to 5/1 of non-ionic/ionic surfactant. The ionic surfactant is mandatory and in amount quite important and this can be an issue as ionic surfactants do have in general negative effects on the over performance of a perfuming composition once applied on the skin.
U.S. Pat. No. 5,468,725 describes an EtOH-free microemulsion, which is defined in a way that makes it difficult to retrieve the ratio of surfactant and perfume and exemplifies a fragrance oil that does not specify how much solvent and oil are in the fragrance—with a 100/2 mixture of non-ionic/ionic surfactant. There is no mention of use of a hydrodrope to decrease the amount of surfactant, and the amount of surfactant used is still considered to be quite high compared to the perfume amount (w/w perfume/surfactant ratio of about 0.38).
Therefore, there is a need for an alcohol-free perfume formulation that is sprayable, stable, transparent, that has moreover a light skin feel as close as possible to the one of ethanol containing compositions, having the lowest possible amount of surfactant and that can contain useful amounts of fragrance oil (which depend on the intended use). Last but not the least, said alcohol-free perfume formulation should advantageously also have a superior profile for fragrance or olfactive delivery. These are requirements needed to satisfy the current need in the perfuming field.